Invert emulsion drilling fluid (commonly called drilling mud) is used when drilling boreholes in the ground, such as for drilling oil or gas wells, etc. It is typically pumped through the drill string and out a nozzle on the drill bit during the drilling of the hole so that the drilling fluid can keep the drill bit cool and carry rock, clay and other solids (commonly referred to as cuttings) removed from the well by the drill bit up the annulus of the well and back to the surface.
Invert emulsion drilling fluids are typically water based or oil based. Oil based muds usually contain oil in the form of a petroleum product similar to diesel fuel. In addition to the oil, these oil based drilling fluids can also contain viscosifiers, weighting agents and other filtrate control additives. To remove the cuttings from the drilling fluid that has been returned to the surface, solids control equipment in the form of shakers, conveyors, centrifuges, etc. are used to remove the majority of the native clays or drill solids that make up the cuttings.
However, these solids control equipment are not designed to re-capture the base oils necessary to create the drilling fluids. It is the presence of hydrocarbons which are physically and chemically bound to the fines, as well as additives, that make separation and recapture through conventional means difficult.